update footer (#1646)

Author: bbejeck

_includes/footer.html

@@ -157,7 +157,7 @@
           target="_blank" rel="noopener noreferrer" href="https://www.confluent.io/modern-slavery-policy/">Modern Slavery Policy</a> | <a
           rel=" noreferrer" href="/#">Cookie Settings</a></div>
       <p class="copy">
-        Copyright © Confluent, Inc. 2014-<span>2021</span>. Apache, Apache Kafka, Kafka, and associated open source
+        Copyright © Confluent, Inc. 2014-<span>2023</span>. Apache, Apache Flink, Apache Kafka, Flink, Kafka, and associated open source
         project names are trademarks of the
         <!-- --> <a target="_blank" rel="noopener noreferrer" href="https://www.apache.org">Apache Software
           Foundation</a>